See
http://www.t-mobile.com/coverage/
NC has 1900 roaming with Cingy. You have to go to KY or WVA.
On the Moto site, all i could find was the TRIBAND manual.
HOWEVER, on Ebay, they SAY they have "new" L6s that are quad-band. Cannot confirm this other than pointing you to Ebay and you have to BELIEVE the claims. It certainly is POSSIBLE that they would for the US market bring out a quad-band.
Best I can do for you.
Stan